Magneto-optical recording media and devices for recording and reproducing information stored on magneto-optical recording media are generally known. A known magneto-optical recording medium is the magneto-optical disc, which is also denoted as MOD or MO and in which there is arranged behind a transparent layer a magneto-optical layer on which information or data are stored and from which the stored information or data can be read. In order to store or write information or data onto a magneto-optical disc, the magneto-optical layer is heated by a laser beam, focused onto the disc, to a temperature in the region of the Curie or compensation temperature. Arranged behind the disc is an electromagnet which magnetizes the region heated by the laser beam in one direction of magnetization or the other. A magneto-optical writing device therefore comprises an optical scanning device which co-operates with an electromagnet and is denoted as a pick-up. After the laser beam is switched off, the heated site cools off again below the compensation temperature, and the direction of magnetization fixed by the electromagnet is maintained. It is, so as to say, frozen. In this case, one direction of magnetization corresponds to a logic one while the opposite direction of magnetization represents a logic zero.
The information or data are read using a principle which is based on the Kerr effect and on the fact that the plane of polarization of a linearly polarized light beam is rotated by an angle in the case of reflection at a magnetized mirror. The plane of polarization of the reflected light beam is rotated to the right or left in accordance with the direction of magnetization of the mirror. The rotation of the plane of polarization of the light beam reflected by the disc is detected by an optical scanning device, and a corresponding information or data signal is generated.
Provided for the purpose of magnetizing the magneto-optical layer is an electromagnet which can magnetize a region which is swept over by an optical scanning device. Magneto-optical recording devices are known in which information or data already stored on the recording medium must be erased before new information or data can be recorded. For this purpose, the magneto-optical layer is heated by the laser up to the Curie or compensation temperature at the sites at which the new information or data are to be stored, and magnetized in one direction. The plate is initialized. The laser power is switched between a small and a large value as a function of the bit to be stored so as to record the new information or data. For example, if a logic zero is stored at the previously erased site, the laser operates at the low power so that the Curie or compensation temperature is not reached. For the purpose of recording a logic one, by contrast, the laser heats the new site to be written on up to the Curie or compensation temperature so that said site can be remagnetized.
By contrast with this, there are also already known magneto-optical recording devices in which already stored information or data are directly overwritten on the recording medium without firstly having to be erased. For the purpose of reliable remagnetization, this method presupposes a high field strength which must be changed over at high speed in order to record new information or data. Since changing over high field strengths at high speed leads in a known way to intense heating of the electromagnet, the data rate up to which this method can be applied is limited. A very high data rate such as required, for example, to store a television signal would lead to impermissible overheating of the write head. In order to store new information or data at a high data rate on a magneto-optical recording medium already written onto, it is therefore necessary for the stored information or data to be erased in advance in accordance with the abovenamed method. For this purpose, before recording it is necessary to provide a time consuming erasing pass, which can be carried out by the magneto-optical writing device provided for recording information or data. In order to permit information or data to be recorded immediately, there is therefore a need for an additional magneto-optical writing device which can then be used to erase in advance information or data already recorded on the magneto-optical recording medium. The magneto-optical recording medium is then initialized by the magneto-optical writing device, also denoted as an erase pick-up.